1. Field of the Invention
The present invention relates to a device for detecting rotational position deviation, which detects the deviation of the rotational position of machine axes driven by electric motors with pulse signals, which are outputted from pulse generators according to the rotation of the electric motors. It also relates to a device for detecting rotational position deviation in order to precisely synchronously control axes driven by plural electric motors.
2. Description of the Related Art
FIG. 6 shows an example of a conventional device for detecting rotational position deviation. In FIG. 6, 1 and 2 are machine axes, 5 and 6 are electric motors, 7 and 8 are two-phase (A phase and B phase) pulse generators having zero phase which are attached to the electric motor axes, 9 is an A phase signal, 10 is a B phase signal and 11 is a zero phase pulse which is outputted by each one rotation of electric motors 5 and 6.
12 is a device for detecting rotational position deviation, and 13 and 14 are pulse transducers transforming two pulse trains which are outputted from the pulse generators 7 and 8 into one pulse train. The pulse transducers 13 and 14 output pulse train signals 17 according to the rotation of the electric motors 5 and 6. Further, 15 and 16 are regular/inverse rotation detectors, which detect regular or reverse rotation of the electric motors 5 and 6, and output the rotational direction. signal 18.
19 and 20 are integrating counters counting up or down the pulse train signals 17 according to the rotational direction signal 18 and clearing them by zero phase pulse 11.
25 is a calculator of rotational position deviation detecting the deviation by calculating the output 21 of the integrating counters 19 and 20, and its output 26 is used, for example, for synchronous control of an induction electric motor (not shown).
FIG. 7 shows an action of the device for detecting rotational position deviation of FIG. 6, as follows. The action of FIG. 6 is explained by referring to FIG. 7. FIGS. 7(a) and (d) show output pulses from the pulse transducers 13 and 14, (b) and (e) show zero phase pulses from the pulse generators 7 and 8, and (c) and (f) show count outputs of the integrating counters 19 and 20.
As shown in FIG. 7, the integrating counters 19 and 20 count the output pulses from the pulse transducers 13 and 14, and they are cleared when the zero phase is outputted, and recount output pulses from the pulse transducers 13 and 14 again.
Accordingly, the counted values of the integrating counters 19 and 20 correspond to the rotation angle of the pulse generators 7 and 8. For example, in FIG. 7, when the counted values of the integrating counters 19 and 20 at time t0 are a3 and a4 respectively, the rotation angles of the pulse generators 7 and 8 at time t0 are each a3/a1xc3x972xcfx80 and a4/a2xc3x972xcfx80, where the number of pulses by one rotation counted from the zero phase pulse are a1 and a2, respectively.
That is, the counted values a3 and a4 of the integrating counters 19 and 20 show the rotation angles of the pulse generators 7 and 8. The counted values of the integrating counters 19 and 20 are inputted into the calculator of rotational position deviation 25. The calculator of rotational position deviation 25 calculates the rotational deviation of the electric motors 5 and 6 and outputs it as deviation output 26.
However, consider, for example, a case for accurately synchronously controlling two machine axes connected to the electric motors. When a deceleration mechanism is attached to one electric motor, which is connected to the machine axis, or both electric motors employ deceleration mechanisms, the machine axes connected to the electric motors are not precisely controlled synchronously, even if the deviation is measured by calculating the count output of the integrating counter. The present invention is originated by considering the above-mentioned points.
An object of the present invention is to solve the problems and provides a device for detecting rotational position deviation, which can control synchronously the machine axes driven by the electric motors even if they have a deceleration mechanism with any deceleration rate.
The device for detecting rotational position deviation of the present invention detects rotational position deviation of machine axes driven by electric motors with pulse signals, which are outputted, from pulse generators of incremental systems, which are attached to at least two electric motors.
Further, the present invention comprises the following components.
At least one deceleration mechanism between an electric motor and a machine axis comprises a pulse transducer transforming two pulse trains that are outputted from the pulse generators, into one pulse train. Further, it comprises an integrating counter corresponding to the electric motor, calculating a pulse train that is outputted from the above-mentioned pulse transducer corresponding to the rotation angle, and clearing them by the zero phase pulse that is outputted by each one rotation of the pulse generator. Also, it comprises a count transducer transforming the count output from the integrating counter. Furthermore, it comprises a rotational position deviation calculator outputting a rotational position error by calculating outputs from the integrating counter and count transducer.
The count transducer transforms the count output of the integrating counter to the count value corresponding to the deceleration ratio of said deceleration mechanism, and outputs it to the rotational position deviation calculator.
In the present invention, as the count transducer is employed and the count output of the integrating counter is transformed to the count value corresponding to the deceleration ratio, the machine axes are precisely synchronously controlled, even if the deceleration mechanism with a different deceleration ratio is attached between the electric motor axis and the machine axis.